1. Field of the Invention
The present invention relates generally to a machine tool and more particularly to an improved machine tool provided with a turret head rotatably supporting a plurality of tool spindles.
2. Description of the Prior Art
In a machine tool having a frame, a turret head rotatably mounted upon the frame, and a plurality of tool spindles rotatably supported within the turret head, each of the tool spindles being capable of being positioned at an operative position by the indexing movement of the turret head, generally rotating motion of the tool spindle positioned at the operative position may be performed by means of power drive means carried by the frame and coupling means which includes first coupling means mounted upon each tool spindle and second coupling means mounted within the frame and adapted to engage with the first coupling means of the tool spindle positioned at the operative position. It does not always follow that the first coupling means engages with the second coupling means in a fixed angular relationship to each other.
Accordingly, in order to perform the angular positioning of the tool spindle positioned at the operative position, an angular positioning mechanism, such as a set of notch and plunger, for the exclusive use of each of the tool spindles, has to be mounted within the turret head so as to directly position the respective tool spindle. In the conventional machine tool, a plurality of actuators, such as cylinder mechanisms, for actuating the respective angular positioning mechanisms had been mounted within the turret head, which had resulted in the disadvantages that the turret head becomes large in size and hydraulic circuits for conducting hydraulic fluid from a pump provided within the frame to the cylinder mechanisms become complicated because the turret head is rotatable in relation to the frame.
Moreover, the first and second coupling means generally include toothed coupling members. Such first and second coupling means are incapable of engaging with each other with only a relative axial shifting therebetween, because of teeth thereof butting against each other. Therefore, to perform engagement with each other, there is need for a relative angular inching therebetween. As a result, more time is required to perform engagement between the toothed coupling members and the toothed coupling members are subject to damage due to the butting.